For many decades, critical components such as BOPs have been manufactured using open die forging technique followed by a substantial machining operation.
With traditional open die manufacturing process (ingot-pin forming and saddling, upsetting, drawing, and forging to size) such large and critical components are manufactured with a material yield of approximately 40% to 45%. Broad steps involved in a typical existing forging method for manufacture of such parts are:
Ingot cogged into bloom→saw cutting→rough sizing→rough machining→heat treatment→semi finish machining→finish machining
As shown in FIG. 2, these involve drawing the fluted ingot, upsetting, cogging and cutting it in 2 pieces, followed by machining, heat-treating and finish-machining.
The above process entails achieving a rough forging shape by the open die forging process while final shape and dimensions are achieved through the machining. In a nutshell, the existing manufacturing method is the combination of open die forging, machining and heat treatment. It has been the applicant's experience that the existing process results in about 42% utilization of material (or about 58% wastage of material) over the entire process: right from cogged bloom to finished part.
One of the key issues observed in adopting conventional open die forging methods to forge large components such as a BOP is fish-tail forming as illustrated in FIG. 4. At the end of a cogging step, an ingot with rectangular end configuration is obtained. When the rectangular end shape is forged using an open die method, the material at the periphery starts to move ahead of the material near the centre, thus forming a fish tail at end shape of cogged billet.
In an open die forging process for manufacturing large and critical component such as a BOP, there are no existing processes which allow forming near net shapes (and thereby reduce the extent of machining). Hence there is a need to develop an open die forging process to make complex, large and critical components which will result into reduction in input material, machining operations along with cycle time, energy consumption and ultimately in the manufacturing cost.
It is evident from FIG. 2, during mass production of such components using conventional forging methods, substantial raw material is wasted with conventional manufacturing method which results into large machining time and poor yield (42%). In order to reduce such wastage, it is important to have near-net shape input to machining. This would help establish right balance between forging and machining processes and effectively utilize material and machining time. The components such as a BOP would thus be manufactured with improved productivity without compromising the desired mechanical properties and specific strength.
There have been a number of inventions made in the field of BOPs. Some of these are listed below.
U.S. Pat. No. 8,136,247 includes forming a first billet to form a first portion of the blowout preventer body; forming a second billet to form a second portion of the blowout preventer body; and welding the billets to form the blowout preventer body.
The invention of U.S. Pat. No. 6,318,482 relates to a BOP permitting a certain degree of controlled fluid leakage to the annulus above the packer, whereby drilling mud may be caused to fill up the entire borehole in an emergency situation associated with a dangerous blowout from the subsea well. It is thus clear that Occurrence of an uncontrolled blowout of fluid (liquid and/or gas) in a subsea well, the blowout preventer is released in a manner to adopt an activated or set position stopping the blowout.
U.S. Pat. No. 5,897,094 the present invention relates to blowout preventers (BOPs) which are conventionally used in hydrocarbon recovery operations to prevent well blowouts. More particularly, this invention relates to the BOP with an improved mechanism for structurally interconnecting the BOP body and each of the pair of radially opposing doors which support the ram assemblies, and for structurally disconnecting the doors from the BOP body during ram block service operations.
U.S. Pat. No. 2,284,869 relates to blowout preventers for casing Heads of general type with previous U.S. Pat. No. 19,047 entitled ‘Casing head with blowout preventer” & as one of its principle objective is provision of a relatively simple and inexpensive but nevertheless extremely effective blowout preventer.
U.S. Pat. No. 3,647,174 invention relates to blowout preventers of ram type having piston and cylinder means for normal opening and closing of the rams and for also effecting movements of the preventer bonnet away from and back to body when bonnet is disconnected from body.
U.S. Pat. No. 4,044,988 invention relates to blowout ram preventer comprising housing with a longitudinal cavity and a transverse bore. Rams arranged in the cavity of housing to reciprocate relative to bore. The transverse spacing between longitudinal guides at walls of the cavity is uniformly reduced in direction from ends of housing to the bore, the ram packer being reinforced from the bore side with radial metal members while the body of ram is comprised of a plurality of member adapted to move relative to one another during ram movement.
U.S. Pat. No. 4,227,543 invention relates to an improved blowout preventer having a secondary sealing system which can be used to stop leaking through the packing, also providing secondary sealing capability available whenever there is a leak.
U.S. Pat. No. 4,253,638 invention relates to an improved blowout preventer in which the bonnets are pivotally mounted to the body and are secured by a throw-type latch. The hinges and latches are made adjustable so that the bonnet sets properly on the body in closed position.
U.S. Pat. No. 4,526,339 the present invention is directed to blowout preventer of the cross ram type where first and second pairs of rams on the same plane provide for flexibility. The invention is particularly used in the drilling of oil and gas wells and related services; i.e., snubbing and work over.
U.S. Pat. No. 4,844,406 this invention relates to well tools, and to a device for installation on the tubing head at the top of a well to confine pressure in the well, and more commonly known as blowout preventer. The blowout preventer of the invention is constructed to provide a seal at upper end of a well about a tubing string, a polished rod, a wire line, and to close off the bore through the well head in the absence of any of the members extending through the wellhead.
It is evident that none of these deal with the problem of raw material wastage during the manufacturing process or with improving the component quality. There is therefore a need to provide a manufacturing process for large and critical components such as BOPs which achieves effective material utilisation. In particular there's a need to provide a manufacturing process with combination of open die forging or close die forging and machining. Furthermore, the industry finds a need for a manufacturing process that would achieve a near-net shape before carrying out finished machining.